Brake control system



July 21, 1936. v s G DOWN 2,048,325

BRAKE CONTROL SYSTEM Filed June 5, 1935 INVENTOR ATTORNEY SIDNEY 6.DOWN.

Patented July 21, 1936 PATENT OFFICE This invention relates to brakecontrol systems, and more particularly tobrake systems for high speedrailway trains'and traction vehicles.

Safety considerations require that where trains and traction vehiclesare to be operated at high speeds a braking equipment must be providedwhich combines a highdejgree of reliability with flexibility of control.A good example .of such a braking equipmentis that described and claimedin the application of Ellis EfHewitt; Serial No. 741,063, filed August23, 1934, for a Brake equipment, which application isowned by theassignee of the present application. V In the braking equipmentfillus'trated in the Hewitt application 'a retardationcontroller deviceis provided for limiting the maximum rate of retardation which may beproduced by an application of the brakes to avalue which will notproduce sliding of the wheel's' The type of retardation controllerdevice there "shown is of the pneumatic type, operating a valve forcontrolling the pressure of fluid supplied through a control pipe. Ipropose to provide animproved form of retardation controlling mechanismadapt:- able for use with braking equipments of the type illustrated inthe Hewitt application.

i "In this connection, I propose to providea re;-

tardation controller device of thefelectric. type,

and mechanism associated therewith for controlling the pressure of fluidin a control pipe, so as to prevent the rate of retardation produced bybraking from exceeding a'chosen maximum value.

The electric type retardation controller device has certain advantagesover the pneumatic, type, in that it is more easily adjusted, (anteadjusted for finer increments of control, and willi re'tain itsadjustment longer underivarying conditions. Another advantage oftheelectric type is thatit perrnitsjthe employment of a simpleiormjofindieating means for indicating when the retardation controllerdevice has operated. The indicating means may be located in theoperatorsbooth or cab, ','where he is informed by "such whenthe retardationcontroller device has' operated. .1 1

It is therefore a principal objectof the [resent inventionto provideanjimproved iormlof retard- :ation controlling mechanism adaptable'foruse with braking" equipment intended for use with high speed trains, andtraction vehicles. a

A further object of thejpresent invention is to 7 provide a novel,arrangement of specific apparatus for carrying outthe aforementionedobject. 7'

I Other objects and advantages of the, invention :will appear more fullyfrom the, following description, which is taken in conn'ectionwlthth'e,Tat-

tached drawing, wherein there is shown in diagrammaticand schematic forma simplified .embodiment of theinvention.

' While the embodiment of the invention illus-' trated in the drawinghas been shown in simplifled form, it will :be apparent as thedescription proceeds that the invention may be readily adapted tovarious types of high speed train braking equipments, and particularlyto a. type such as that "disclosed in the aforementioned Hewittapplication.

Considering briefly at first the embodiment illustrated, there isprovided a brake cylinder l0 and a magnet valve device l2 forcontrolling the supply of fluid'under pressure to and its release fromthe brake cylinder. A supply reservoir 13 provides a local supply offluid under pressure. .It is to be here understood that in adapting theembodiment illustrated to a train, at least one brake cylinder ID, amagnet valve device I2, and

a supply reservoir I3, are provided on each car inhthe train, while theother parts about to be referred to 'ne'ed'only be provided on. the headend or control car.

devices I Z throughout the train, there is provided a pneumatic controlswitch M. For manually controlling operation of the switch device 14,

to efiect anapplic'ation of the brakes, there is provided a brakevalvedevice l5 and a control reservoir 16.

For controlling the rate of retardation of the train produced by anapplication of the brakes,

fsoias' to prevent the rate from exceeding a chosen maximum value, thereare provided a retardation controller device l8 and a control valvedevice l9. .Indicating devices 20 and 2| are provided to indi- Jcateoperation of the retardation controller de- ,vice l8. p

A .A main reservoir 22 is provided as themain source of supply of. fluidunder pressure, and a feed valve device 23, which is of conventionaltype, regulates the pressure of fluid supplied from thernain reservoir.

Considering now in deta1l the devices above valve21 urged toward aseated position by a that portion which when energized actuates theenurnerated, the magnet valve device I2 is embodied ina casing and isprovided withanapplication portion 25 and a release portion 26.

The application portion 25. consists of a supply spring, 28, and towardan unseated position by action of an electromag'net in the upper part'ofply reservoir l3, past the unseated valve 21, to a brake cylinder pipe29, to which the brake cylinder I is connected. When the supply valve2'! is seated, this flow of fiuid is cut off.

5 The release portion 26 consists of a release valve 30 urgedtoward aseated position by a spring 3|, and toward an unseated position byaction 'ol an electromagnet in the u per part of the casing or thisportion, which when energized actuates the valve downwardly. When thevalve 30 is in unseated position, a communication is established betweenthe brake cylinder pipe 29 and the atmosphere, past the unseated valve30, and through port 32.

is seated, this communication to "the-atmos'phere is cut oil.

The pneumatic control switch l4 isembodied in a casing provided with twopressure tight chambers 34 and 35 separated by a flexible diaphragm .36;Secured to the diaphragm 36 are upper and letter stems 3'! and -38,respectively. Movement of "the diaphragm 36 controls through these twostems opening and closing of a set of application contacts and a set ofrelease contacts 4| U The diaphragm '36 is normally flexed upwardly togm'ainftain closed release contacts '41. Closing of "these contactsestablishes a' circuit rrem "a battery 44 tothe'eIectromagnet in the-release portion ZBof the magnet valve device "[2, by way of a conductor45, contacts 4|, and tr'a'ih 'wire '46. The return circuit to battery 44is'by'w'ay "or greats estimation "41.

when fluid funderpressure is supplied "to the chamber 34, the diaphragm36 is flexed downwardly too'pen contacts 4'1 and'to then close contacts40. Opening of "contacts '41 deeher'gizes the eie'etromagnt in therel'e'ase portion 26, while closing of contacts "40 elfe'ctsenergization of "the application portion 25, Train batter "44, through40 7a circuit which includes conductor '48, contacts aa natrain wire 49,The returnpircuit to the I pattery atis Hy wayo'f the aforementionedground c'or'inection 41;

. When fluid under pressureis' supplied to the 4 fcha'mbe'r35 to "adegree slightly below the degree of pressure in the upper chamber 34,diaphragm '36 will move upwardly to "a position where both jc'on'tactsto "and 41 'are'op'en. Both the application portion '25 and the releaseportion 25, of the magfietvaive' device '12, will then hedee'lierg'l'z'ed.

r If the pressure of the fluid in the lower chamber senses; to e valuesubstantially equal "to or greater than the pressureof fluid the upper'jdhahrber "3'4, diaphragm 36 will "mov upwardly -5 "to close contacts4| "to again energize the release or s:- i a The supplyof fluid underpressure to the upper chamber 34; in the pneumatic control switch-devicel 4 is controlled by the brake valve device l-s. brake valve device isillustrated as beme "of the self-lapping type, and {is embodied inafcasing defi ning "a pressure chamber -50, Torcontrollihg the supply(ff fluid under pres- 7 sure to the pressure chamber 5Dfthere isprovided 1 asuppiy valve {51 urged toward-a seated position b'y'sp'rihgp When the supply valve 5| is unseated, fluid under pressure flows fromthe feed valvedevice 23, through pipe and passage 53,

p'ast the unseated supply "valve 51 to the pressure s *ch'amber'50. Y v

p 1 Disposed in a chamber 54 in the valve device easing, is a rnovab'leabutment 55 in the form of a piston having i'riteriorly thereof -'arelease valve 56 urged toward an 'ui'iseated {position b'y a spring"57-; When'the-release valve 56 unseated po- When the valve 30 sen essition, a communication is established between the pressure chamber 50and the atmosphere, by way of passages 58 and 59, piston chamber 54 tothe right of the abutment 55, and exhaust passage 60. When the releasevalve 56 is in seated 5 position, this communication is cut off.-

The movable abutment 55 is subject on its left hand side "to pressure offluid in the chamber 50, and on its rigl it hand side to pressure of aregulating spring 6|. Tension on the regulating 10 spring is regulatedby an adjusting member 52.

A set screw 63 is provided in the regulating memhe'r62, itr "engaging aplunger 64 associated with :the movable abutment 55, to limit the travelof the movable abutment to the right. 15 Fo'r controlling seating andunseating of the supply valve 5| and release valve 56, there is provideda mechanism including spaced levers 66 pivotally secured at 61 to andcarried by a slidable pivot carrier -68 disposedin a bore 69 in 20 thecasing. Between the met ends of the spaeed lever ttthereisrdtatebiycarries afr'ollei' T0 for engaging "the'st'm "of release 'valve '56.Lee'seiy held btwe'en'th e upper ends of the spaced Ie'v'ers ts is astem" 1] for "engaging "the "su ply valve "51. 25

when the silicate pivot c'a'rr'ier ta is actuated to the light, the saced levers fi fi pivot about their upper ends, while the lower enus"swih'g inwardly to the r iease valve '56, 'due to 'the 'suppiyvalve'spring 52 being heavier than the release so vaivesprm'g 51. it'ssoon asthe release valve 56 is seated, the spaced levers "66 pivot abouttheir lower ends and the upper ends to the right to'unseatthe supply VaI During this movet. ment the regulating ring 61 is 'una'ppreci'ably atcompressed, because "it heavier than either or both of the twospnngsjflahd 51.

With the releaseyal've 56 seated and supply 'vaive =5| unseated, fluiduiide'niiieswi win flow to the pressure chamber 50. when the pressure of"thejluid rises it "acts upon *the movable abutment '55 to actuate'it tothe right. When the 'movable abiitineiit has been actuated sufficiently'tofthe "right, "supply spring 52 "will seat "supply w Valve 51 to lap"the supply t'o'the pressure j'chami ber50, If the pressure in thechamber '50 has reachedavalu'e high enou h toactuatethe m'ovabl'eabutment "55 further to the right, release valve 55 will attest to'releas'eiluid "under pressurefrom the pressure chamber '50, until the'0 'degree o'f fpressme drops to the point where the release valve 5 56is again seated.

A little thought will show that the pressure finally ex st ng in "thepressure chamber 50 will w *correspondtb the degree 'of movement of the'5 slidable pivot'caifrie'r -68 to the right. i

v For actuat ng the pivot carrier '68 to the right, there isiprovideda-cain T3 secured to "an'operat'ing shaft 14, which isrotatable upon movement of e handle. 15, Whe'n't-lre handle 15 is movedfrom 5 faiel easefposition'into tin-application zone, cam 13 "isrotated. The peripher of cam '13 'is such that as it rotates, itprogressively moves the pivot'carrier 68 '"tothie Tight. Since the'p'ressur'e'of fluid. v "suppliedto the pressure chamber corresponds '5tothe position of the pivot carrier 68, it follows that the pressure of'fluid in the pressure chamber 50 will also'correspond to the degree ofmovement of the handle into the application zone.

When the handle 15 is turned back to release "71 position, the pivotcarrier 68 will be returned to its extreme left hand positionbyactio'no'f 'o'neo'r more of the springs 52, '51 and BI, so that fiuid'nder'pre'ssure is released fromthe chamber 50-to e the'atniosphere. J

The retardation controller device I8 may be of one of a number of types,and I have therefore illustrated this device in diagrammatic form only.As there shown, the device comprises a pendulum 11 pivotally secured at18 to a supporting casing 19, and having at its lower extremity a body80. The pendulum 11 is disposed on the head end vehicle in a manner suchthat when the vehicle and train are decelerating, the inertia effect onthe body 88 causes the pendulum to swing to the left a distancecorresponding to the rate of deceleration.

The body 80 carries a contact 8| insulated therefrom, which contact isadapted to successively engage stationary and resilent contacts 82 and83, disposed in the path of movement of the contact 8 I.

The contact 82 is adapted to be engaged by the movable contact 8Islightly ahead of the contact 83. Therefore, since the inertia effect onthe body 88 is proportional to the rate of retardation of the vehicle ortrain, contact BI will engage contact 82 at one rate of retardation, andwill engage contact 83 at a slightly higher rate of retardation.

The control valve device I9 comprises an inshot valve portion and amagnet valve portion 85. The inshot valve portion consists principallyof a ball valve 81 normally held in unseated position by a piston 88through a stem 89. A spring 90 urges the piston 88 upwardly, and thetension of the spring is adjustable through an adjusting nut 9I.

The piston 88 is subject on its upper side to pressure of fluid suppliedto a chamber 92, and when the pressure of this fluid has reached apredetermined value, piston 88 will have been actuated downwardly farenough to permit ball valve 81 to seat.

The magnet valve portion 85 comprises a cutoif valve 94 urged toward anunseated position by a spring 95 and toward a seated position by actionof an electromagnet in the upper part of the casing, which whenenergized actuates the valve downwardly.

The magnet valve portion 88 is also provided with a release valve 95,which is urged toward a seated position by action of a second'spring 91,and toward an unseated position by action of a second electromagnet inthe upper part of the casing, which when energized actuates the valvedownwardly.

The control valve device i9 is connected to the pressure chamber 58 inthe brake valve device I5, by way of a pipe 99. Therefore, when fluidunder pressure is supplied to the pressure chamber 50, it flows throughpipe 99, passage I90, past the unseated ball valve 81, through pipe andpassage It I,

to both the control reservoir I6 and the upper chamber 34 in thepneumatic control switch I4.

When the pressure of the fluid thus supplied reaches a value at whichball valve 81 is seated, it then flows around the seated ball valvethrough passage I92, past the unseated cut-ofi valve 94, and from thencethrough passage I83 and pipe and passage I8I to the control reservoir I6and upper chamber 34. The purpose of the inshot valve portion 85 is toinsure that fluid is supplied to the control reservoir I6 and upperchamber 34 to a predetermined degree should the cut-ofi valve94 beaccidentally seated. 7

If while both the ball valve 81 and the cut-ofi valve 94 are seated, therelease valve 96 is unseated, fluid under pressure will be released fromthe control reservoir I6 and the upper chamber 34 to the atmosphere, byway'of a choke I05, past the unseated release valve 96, through passageI06, and a safety valve device I01. The safety valve device I81 is ofconventional design, and is provided to prevent a release of fluid belowa predetermined pressure, so that in case the release valve 96 should beaccidentally stuck in an open position all of the fluid supplied to thecontrol reservoir I6 and upper chamber 34 will not be lost to theatmosphere.

The operation of this embodiment of my invention is as follows:

Operation When the train is running the brake valve handle 15 ismaintained in release position. The parts of the brake apparatus willthen be in the positions shown in the drawing. The supply reservoir I3on each car in the train will be charged from a main reservoir pipe I88,which connects with thefeed valve device 23., through a choke I09 and acheck valve device H2. The check valve device I I0 permits flow of fluidonly in the direction indicated by the arrow.

With the other parts in the positions as shown, the brake cylinder In oneach car will be connected to the atmosphere, past the unseated valve 30in tlzie release portion 26 of each magnet valve device When it isdesired to effectan application of the brakes, the brake valve handle 15is moved into and unseating of supply valve 5| in the brake valve handleeifects seating of release valve 55 and unseating of supply valve 5! inthe brake valve device I5. Fluid under pressure is then supplied to thepressure chamber 58 to a degree according to the degree of movement ofthe handle 15. From the pressure chamber 58, fluid flows through pipe99, passage I90, past unseated ball valve 81, and pipe and passage ill!to control reservoir I6 and upper chamber 84 in the pneumatic switchcontrol device I4. The control reservoir I6 is provided to add volume tothe system, so that the pressure in chamber 34 may be varied in finerincrements. Diaphragm 36 is then actuated downwardly to open releasecontacts 4| and to then close application contacts 40.

Opening of contacts 4i deenergizes the release electromagnet in eachmagnet valve device I2, to efiect seating of the release valve 38,thereby closing communication between the brake cylinde I8 and theatmosphere.

Closing of application contacts 48 effects en ergization of theapplication portion 25 of the magnet valve device I2, to unseat valve21, and therebypermit fluid under pressure to flow from supply reservoirI3 to the brake cylinder I8.

As soon as the pressure of fluid supplied to the control reservoir I6and upper chamber 84 reaches a predetermined value, inshot piston 88will move downwardly far enough for ball valve 81 to be seated. .Fluidthen flows through the bypass communication through the magnet valveportion 85, as before described. The inshot valve mechanism insures thata pressure will be established in the switch chamber 34 to a degreesufficient to apply the brakes, so that if the cutofi valve 94 isaccidentally seated the train will be stopped.

Fluid flowing to the brake cylinder IE! on each car also flows throughpipe 29 to the lower chamber 35 in the switch device I4, so that as thepres- .phragm 36 will move upwardly to open contacts 75 40, while stillmaintaining contacts M open. The application portion '25 of the magnetvalve-device 12 will then be deenergized, and supply valve 2'! will beseated by spring 28. The supply of fluid under pressure to the brakecylinders l0 will then be lapped at a pressure corresponding to-that offluid supplied to chamber 3 'As the pressure of fluid builds up in thebrake cylinder 53 on each car, the train will then begin to decelerate.If the rate of retardation is high enough to cause pendulum ll to swingfar enough to the left for contact M to engage contact 82, the

cut-off electromagnet in the control valve device l9 will be energizedto effect seating of the cutoff valve '94. Further supply of fluid underpressure to the control reservoir l8 and upper chamber 3 will then beprevented.

As the train decelerates with the brakes thus lapped, the rate ofretardation will increase due to the increase in coeificient of frictionbetween the rubbing parts of the brakes. Therefore, pendulum ll willswing further to theleit and contact 8! will engage contact 83. Whenthis takes place the release 'electromagnet in the control Valve device59 will be energized and release ivalve'ilfi will be unseated. Fluidunder pressure is then be energized to effect unseating of release valve35;. Fluid under pressure will then be released from each brake cylinderiii to the pherapast the unseated release valve 3?: and through exhaustport 32.

As the brake cylinder pressure is thus diminish ed, the rate ofretardation decreases and pendui" n ll swings to the right. As contact83 disengages from contact 83, the release electromagnet in the controlvalve device will be deenergized, release valve 95 will seat, and therelease of fluid under pressure from the control reservoir l6 and upperchamber 36 will be terminated. The pressure in the brake cylinders itwill continue to diminish until the pressure in lower chamber 35 becomesequal to or slightly below the pressure in upper chamber 34, whereupondiaphragm 3t will move downwardly and open contacts i l. The releaseelectromagnet in each magnet valve device l2 will then be deenergized,release valve 35! will be seated, and the brake cylinder pressure willthen again be lapped.

It will thus be apparent that as the train decelerates, the pendulum itwill move backward and forward to cause periodic engagement betweencontacts 35 and 83, whileh'olding engagement with the contact 82, tointermittently effect a release or fluid under pressure from the brakecylinder it on each car.

As contact 8! engages contact 82, the indicating device 2! will effectan indication so that the operator will know that the supply of fluid tothe control reservoir l6 and upper chamber St has been cut ofi. Ascontact 3! engagescont'act 8E, the operator will be informed that therelease of fluid under pressure from these two volumes fluid supplied tothe control reservoir l6 and upper chamber 34, the indicating devices 20 and -21 will .so'inform the operator. The operator may then leave thebrake handle 15 in fu-llapplication position without danger of causingwheel sliding.

If a light application of the brakes is desired, such that theretardation controller device I8 will not become effective incontrolling the application, it will then "be apparent that thepneumatic switch device H3 will function according to the pressure offluid established in the pressure chamber. 5?), to in turn effect apressure in the brake cylinder Ill on each car to a correspondingdegree.

When however the application has been to a degree such that theretardation controller 18 assumes control, and the brake valve handleremains in application position, the train will be decelerated at amaximum rate to a stop. When the train comes to a rest the pendulum Hwill assume its normally vertical position, and a complete release maybe effected.

H0wever, the operator may make a release at any time by simply turningthe brake valve handle '65 to release position, as ball valve 81 willunseat to permit fluid under pressure to be released from chamber 3'3.

While I have illustrated my invention and described it in connectionwith a single embodiment thereof, it is to be understood that I do notwish -to be limited to the exact details shown nor otherwise than by thespirit a-ndscope of the appended claims.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. In a vehicle brake system, in combination, brake means, fluidpressure operated switch means for controlling application of said brakemeans, means for effecting a supply of fluid under pressure to operatesaid switch means, electroresponsive means for controlling said supply,and means operated according to the rate of retardation of the vehiclefor controlling said electroresponsive means.

I 2. In a vehicle brake system, in combination, brake means, a fluidpressure operate-d switch device for controlling application of saidbrake means, means for efiecting a supply of fluid under pressure tooperate said switch device, electroresponsive means operable to cut-offsaid supply, contacts controlling said electroresponsive means, andmeans operated according to the rate of retardation of the vehicle forcontrolling said contacts.

able when closed to effect energization of said electrorespcnsive valvedevice, and means operated according to the rate of retardation of thevehicle for closing said contacts.

4. In a vehicle brake system, in combination, a brake means, a fluidpressure operated switch device for controlling operation of said brakemeans, means for effecting a supply of fluid under pressure toopera'tesaid switch device, a first electrorespcnsive valve means operable 'tocut off said supply, a second electrorespon'sive valve means operable torelease fluid supplied to operate said switch device to diminishthepressure of said supply, contacts for controlling said two CIDelectroresponsive valve means, and a device responsive to the rate ofretardation of the vehicle for controlling operation of said contacts.

5. In a vehicle brake system, in combination, brake means, a switchdevice having a chamber and being operable to control an application ofsaid brake means according to the pressure of fluid supplied to saidchamber, means for efiecting a supply of fluid under pressure to saidchamber, electroresponsive valve means for controlling the pressure offluid supplied to said chamber, contacts for controlling energizationand deenergization of said electroresponsive valve means, and an inertiaoperated device operable at chosen rates of retardation for operatingsaid contacts.

6. In a vehicle brake system, in combination, a brake cylinder,electroresponsive valve means for controlling the supply of fluid underpressure to and its release from said brake cylinder, a switch devicehaving a chamber and contacts operated according to the supply of fluidunder pressure to said chamber for controlling said electroresponsivevalve means, means for effecting a supply of fluid under pressure tosaid chamber, an electrically operated cut-off valve device operablewhen energized to cutoff said supply, an electrically operated releasevalve device operable when energized to release fluid under pressurefrom said chamber, and means operable at a chosen rate of retardationfor energizing said cut-ofi valve device and operable at another rate ofretardation for energizing said release valve device.

7. In a vehicle brake system, in combination, a brake cylinder,electroresponsive valve means for controlling the supply of fluid underpressure to and its release from said brake cylinder, aswitch devicehaving a chamber and contacts operated according to the pressure offluid supplied to said chamber; electroresponsive valve means forcontrolling the supply of fluid under pressure to and its release fromsaid chamber, means governed by the rate of retardation of the vehiclefor controlling said electroresponsive valve means, and means forinsuring supply of fluid under pressure to said chamber to apredetermined degree regardless of operation of said electroresponsivevalve means.

8, In a vehicle brake system, in combination, a V

brake cylinder, electroresponsive valve means for controlling the supplyof fluid under pressure to and its release from said brake cylinder, acontrol reservoir, means for effecting a supply of fluid under pressureto said control reservoir, electroresponsive means controlled accordingto the rate of retardation of the vehicle for controlling the degree offluid under pressure supplied to said control reservoir, a switch devicehaving a movable abutment subject on one side to brake cylinder pressureandon the other side "to pressure of fluid supplied to said controlreservoir, and contacts operated by said movable abutment forcontrolling said electroresponsive valve means.

9. In a vehicle brake system, in combination, a brake cylinder,electroresponsive valve means for controlling the supply of fluid underpressure to and its release from said brake cylinder, contacts forcontrolling energization and .deenergization of said electroresponsivevalve means, a control device having a first chamber and a secondchamber and a movable abutment subject on one side to pressure of fluidin said first chamber and on the other side to pressure of fluid in saidsecond chamber, means controlled by said movable abutment for actuatingsaid contacts, means for supplying fluid under pressure to said firstchamber and for electrically controlling the degree of pressure of thefluid thus supplied according to a chosen rate of retardation, and meansfor supplying fluid under pressure to said second chamber correspondingto the pressure of fluid in said brake cylinder.

10. In a vehicle brake system, in combination, a brake cylinder,electroresponsive valve means for controlling the supply of fluid underpressure to said brake cylinder, a first set of contacts adapted whenclosed to effect operation of said electroresponsive valve means tosupply fluid under pressure to said brake cylinder, a second set ofcontacts adapted when closed to effect operation of saidelectroresponsive valve means to release fluid under pressure from saidbrake cylinder, a casing having a first chamber and a second chamber anda diaphragm disposed between said two chambers for operating said twosets of contacts, means for supplying fluid under pressure to one ofsaid chambers to any chosen degree, means for supplying fluid underpressure to the other of said chambers at brake cylinder pressure, andelectrical means controlled according to the rate of retardation of thevehicle for varying the pressure of fluid supplied to said firstmentioned chamber.

11. In a vehicle brake system, in combination, brake means, a fluidpressure operated switch device for controlling application of saidbrake means, means for efiecting a supply of fluid under pressure tooperate said switch device, electroresponsive means operable to cut offsaid supply,

contacts controlling said electroresponsive means,

means operated according to the rate of retardation of the vehicle forcontrolling said contacts, and means for indicating to an operator whensaid contacts have been operated by said last means.

12. In a vehicle brake system, in combination, a brake cylinder,electroresponsive valve means for controlling the supply of fluid underpressure to and its release from said brake cylinder, a switch devicehaving a chamber and contacts operated according to the supply of fluidunder pressure to said chamber for controlling said electroresponsivevalve means, means for eflecting a supply of fluid under pressure tosaid chamber, an electrically operated cut-ofl valve device operablewhen energized to cut ofi said supply, an electrically operated releasevalve device operable when energized to release fluid under pressurefrom said chamber, means operable at a chosen rate of retardation forenergizing said cut-oil valve device and operable at another rate ofretardation for energizing said release valve device, and indicatingmeans for indicating when each of said electrically operated valvedevices has been energized.

SIDNEY G. DOWN.

